1. Field of Invention
This invention relates to neurotrophic low molecular weight, small molecule N-oxides of heterocyclic esters having an affinity for FKBP-type immunophilins, and their use as inhibitors of the enzyme activity associated with immunophilin proteins, particularly peptidyl-prolyl isomerase, or rotamase, enzyme activity.
2. Description of Related Art
The term immunophilin refers to a number of proteins that serve as receptors for the principal immunosuppressant drugs, cyclosporin A (CsA) FK506 and rapamycin. Known classes or immunophilins are cyclophilins and FK506 binding proteins, or FKBPs. Cyclosporin A binds to cyclophilin A while FK506 and rapamycin bind to FKBP12. These immunophilin-drug complexes interface with various intracellular signal transduction systems, especially the immune and nervous systems.
Immunophilins are known to have peptidyl-prolyl isomerase (PPIase) , or rotamase, enzyme activity. It has been determined that rotamase enzyme activity plays a role in the catalyzation of the interconversion of the cis and trans isomers of peptide and protein substrates for the immunophilin proteins.
Immunophilins were originally discovered and studied in the immune tissue. It was initially postulated by those skilled in the art that inhibition of the immunophilins"" rotamase activity leads to inhibition of T-cell proliferation, thereby causing the immunosuppressive activity exhibited by the immunosuppressant drugs, such as cyclosporin A, FK506 and rapamycin. Further study has shown that the inhibition of rotamase activity, in and of itself, does not result in immunosuppressive activity. Schreiber et al., Science, 1990, vol. 250, pp. 556-559. Instead, immunosuppression appears to stem from the formulation of a complex of immunosuppressant drugs and immunophilins. It has been shown that the immunophilin-drug complexes interact with ternary protein targets as their mode of action. Schreiber et al., Cell, 1991, vol. 66, pp. 807-815. In the case of FKBP-FK506 and cyclophilin-CsA, the immunophilin-drug complexes bind to the enzyme calcineurin and inhibit the T-cell receptor signalling which leads to T-cell proliferation. Similarly, the immunophilin-drug complex of FKBP-rapamycin interacts with the RAFT1/FRAP protein and inhibits the IL-2 receptor signalling.
Immunophilins have been found to be present at high concentrations in the central nervous system. Immunophilins are enriched 10-50 times more in the central nervous system than in the immune system. Within neural tissues, immunophilins appear to influence nitric oxide synthesis, neurotransmitter release and neuronal process extension.
It has been found that picomolar concentrations of an immunosuppressant such as FK506 and rapamycin stimulate neurite outgrowth in PC12 cells and sensory neurons, namely dorsal root ganglion cells (DRGs) Lyons et al., Proc. of Natl. Acad. Sci., 1994, vol. 91, pp. 3191-3195. In whole animal experiments, FK506 has been shown to stimulate nerve regeneration following facial nerve injury.
Surprisingly, it has been found that certain compounds with a high affinity for FKBPs are potent rotamase inhibitors and exhibit excellent neurotrophic effects. Furthermore, these rotamase inhibitors are devoid of immunosuppressive activity. These findings suggest the use of rotamase inhibitors in treating various peripheral neuropathies and enhancing neuronal regrowth in the central nervous system (CNS). Studies have demonstrated that neurodegenerative disorders such as Alzheimer""s disease, Parkinson""s disease, and amyotrophic lateral sclerosis (ALS) may occur due to the loss, or decreased availability, of a neurotrophic substance specific for a particular population of neurons affected in the disorder.
Several neurotrophic factors affecting specific neuronal populations in the central nervous system have been identified. For example, it has been hypothesized that Alzheimer""s disease results from a decrease or loss of nerve growth factor (NGF). It has thus been proposed to treat Senile Dementia Alzheimer""s Type (SDAT) patients with exogenous nerve growth factor or other neurotrophic proteins, such as brain derived growth factor, glial derived growth factor, ciliary neurotrophic factor and neurotropin-3, to increase the survival of degenerating neuronal populations.
Clinical application of these proteins in various neurological disease states is hampered by difficulties in the delivery and bioavailability of large proteins to nervous system targets. By contrast, immunosuppressant drugs with neurotrophic activity are relatively small and display excellent bioavailability and specificity. However, when administered chronically, immunosuppressant drugs exhibit a number of potentially serious side effects including nephrotoxicity, such as impairment of glomerular filtration and irreversible interstitial fibrosis (Kopp et al., J. Am. Soc. Nephrol., 1991, 1:162); neurological deficits, such as involuntary tremors, or non-specific cerebral angina, such as non-localized headaches (De Groen et al., N. Engl. J. Med., 1987, 317:861); and vascular hypertension with complications resulting therefrom (Kahan, et al., N. Engl. J. Med., 1989, 321:1725)
In order to prevent the side effects associated with use of the immunosuppressant compounds, the present invention provides non-immunosuppressive compounds containing small molecule FKBP rotamase inhibitors for enhancing neurite outgrowth, and promoting neuronal growth and regeneration in various neuropathological situations where neuronal repair can be facilitated, including: peripheral nerve damage caused by physical injury or disease state such as diabetes; physical damage to the central nervous system (spinal cord and brain); brain damage associated with stroke; and neurological disorders relating to neurodegeneration, such as Parkinson""s disease, SDAT (Alzheimer""s disease), and amyotrophic lateral sclerosis.
The present invention relates to neurotrophic low molecular weight, small molecule compounds having an affinity for FKBP-type immunophilins. Once bound to these proteins, the neurotrophic compounds are potent inhibitors of the enzyme activity associated with immunophilin proteins, particularly peptidyl-prolyl isomerase, or rotamase, enzyme activity. A key feature of the compounds of the present invention is that they do not exert any significant immunosuppressive activity in addition to their neurotrophic activity. Another significant feature is the novel addition of the oxidation of specific amine groups to the corresponding N-oxide to provide an unexpected increase in bioavailability and potency as compared to compounds lacking the N-oxide group.
Specifically, the present invention relates to a compound of formula I: 
or a pharmaceutically acceptable salt thereof, wherein:
A and B are taken together, with the nitrogen and carbon atoms to which they are respectively attached, to form a 5-7 membered saturated or unsaturated heterocyclic ring containing any combination of CH2, O, S, SO, SO2, NH or NR1 in any chemically stable oxidation state;
W is O, S, CH2, or H2;
R is a C1-C6 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C9 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, or Ar1, where said alkyl, alkenyl, cycloalkyl, or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, and where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 1-indolyl, 2-indolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hyrogen, halo, hydroxyl, nitro, trifluoromethyl, C1-C5 straight or branched alkyl or alkenyl, C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
X is O, NH, NR1, S, CH, CR1, or C(R1)2;
Y is a direct bond, or a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C3-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms or said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR2, S, SO, or SO2, where R2 is selected from the group consisting of hydrogen, (C3-C4)-straight or branched chain alkyl, (C3-C4) -straight or branched chain alkenyl or alkynyl, and (C1-C4) bridging alkyl wherein a bridge is formed between the nitrogen and a carbon atom of said alkyl or alkenyl chain containing said heteroatom to form a ring, wherein said ring is optionally fused to an Ar group; and
Z is an aromatic or tertiary alkyl amine oxidized to a corresponding N-oxide, wherein the aromatic amine is Ar oxidized to a corresponding N-oxide where Ar is a mono-, bi- or tricyclic, carbo- or heterocyclic ring, wherein the ring is either unsubstituted or substituted in one to three position(s) with halo, hydroxyl, nitro, trifluoromethyl, C1-C5 straight or branched chain alkyl or alkenyl, C1-C4 alkoxy, C1-C4 alkenyloxy, phenoxy, benzyloxy, amino, or a combination thereof; wherein the individual ring sizes are 5-6 members; wherein the heterocyclic ring contains 1-6 heteroatom(s) selected from the group consisting of O, N, S, and a combination thereof wherein at least one of the heteroatoms is N, and wherein the alkyl amine is oxidized to a corresponding N-oxide where alkyl is a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C3-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR1, S, SO, or SO2; and,
R1 is hydrogen, (C1-C4) -straight or branched chain alkyl, (C3-C4) -straight or branched chain, alkenyl or alkynyl, or R1 is Y-Z, as defined above.
Another preferred embodiment of this invention is a compound of formula II: 
or a pharmaceutically acceptable salt thereof, wherein:
E, F, G and H are independently CH2, O, S, SO, SO2, NH or NH1;
W is C, S, CH2, or H2;
R is a C1-C6 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C8 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, or Ar1, where said alkyl, alkenyl, cycloalkyl, or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, and where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 1-indolyl, 2-indolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, or phenyl, having one to three substituents which are independently selected from one group consisting of hyrogen, halo, hydroxyl, nitro, trifluoromethyl, C1-C6 straight or branched alkyl or alkenyl, C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
X is O, NH, NR1, S, CH, CR1, or C(R1)2;
Y is a direct bond, or a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C1-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms or said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR2, S, SO, or So2, where R2 is selected from branched chain alkyl, (C3-C4) -straight or branched chain alkenyl or alkynyl, and (C1-C4) bridging alkyl wherein a bridge is formed between the nitrogen and a carbon atom of said alkyl or alkenyl chain containing said heteroatom to form a ring, wherein said ring is optionally fused to an Ar group; and
Z is an aromatic or tertiary alkyl amine oxidized to a corresponding N-oxide, wherein the aromatic amine is Ar oxidized to a corresponding N-oxide where Ar is a mono-, bi- or tricyclic, carbo- or heterocyclic ring, wherein the ring is either unsubstituted or substituted in one to three position(s) with halo, hydroxyl, nitro, trifluoromethyl, C1-C5 straight or branched chain alkyl or alkenyl, C1-C4 alkoxy, C1-C4 alkenyloxy, phenoxy, benzyloxy, amino, or a combination thereof; wherein the individual ring sizes are 5-6 members; wherein the heterocyclic ring contains 1-5 heteroatom(s) selected from the group consisting of O, N, S, and a combination thereof wherein at least one of the heteroatoms is N, and wherein the alkyl amine is oxidized to a corresponding N-oxide where alkyl is a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C3-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR1, S, SO, or SO2; and,
R1 is hydrogen, (C1-C4) -straight or branched chain alkyl, (C3-C4) -straight or branched chain alkenyl or alkynyl, or R1 is Y-Z, as defined above.
Another preferred embodiment s a compound of formula III: 
or a pharmaceutically acceptable salt thereof, wherein:
E, F, and G are independently CH2, O, S, SO, SO2, NH or NR1;
W is O, S, CH2, or H2;
R is a C1-C6 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C8 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, or Ar1, where said alkyl, alkenyl, cycloalkyl, or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, and where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 1-indolyl, 2-indolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hyrogen, halo, hydroxyl, nitro, trifluoromethyl, C1-C6 straight or branched alkyl or alkenyl, C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
X is O, NH, NR1, S, CH, CR1, or C(R1)2;
Y is a direct bond, or a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C1-C3 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR2, S, SO, or SO2, where R2 is selected from the group consisting of hydrogen, (C1-C4) -straight or branched chain alkyl, (C1-C4) -straight or branched chain alkenyl or alkynyl, and (C1-C4) bridging alkyl wherein a bridge is formed between the nitrogen and a carbon atom of said alkyl or alkenyl chain containing said heteroatom to form a ring, wherein said ring is optionally fused to an Ar group; and
Z is an aromatic or tertiary alkyl amine oxidized to a corresponding N-oxide, wherein the aromatic amine is Ar oxidized to a corresponding N-oxide where Ar is a mono-, bi- or tricyclic, carbo- or heterocyclic ring, wherein the ring is either unsubstituted or substituted in one to three position(s) with halo, hydroxyl, nitro, trifluoromethyl, C1-C6 straight or branched chain alkyl or alkenyl, C1-C4 alkoxy, C1-C4 alkenyloxy, phenoxy, benzyloxy, amino, or a combination thereof; wherein the individual ring sizes are 5-6 members; wherein the heterocyclic ring contains 1-6 heteroatom(s) selected from the group consisting of O, N, S, and a combination thereof wherein at least one of the heteroatoms is N, and wherein the alkyl amine is oxidized to a corresponding N-oxide where alkyl is a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C3-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with C, NH, NR1, S, SO, or SO2; and,
R1 is hydrogen, (C1-C4) -straight or branched chain alkyl, (C3-C4) -straight or branched chain alkenyl or alkynyl, or R1 is Y-Z, as defined above.
A further particularly preferred embodiment of this invention is a compound of formula IV: 
or a pharmaceutically acceptable salt thereof, wherein:
n is , 1, 2 or 3 forming a 5-7 member heterocyclic ring;
W is O, S, CH2, or H2;
R is a C1-C6 straight or branched chain alkyl or alkenyl group optionally substituted with C3-C8 cycloalkyl, C3 or C5 cycloalkyl, C5-C7 cycloalkenyl, or Ar1, where said alkyl, alkenyl, cycloalkyl, or cycloalkenyl groups may be optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, and where Ar1 is selected from the group consisting of 1-napthyl, 2-napthyl, 1-indolyl, 2-indolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, or phenyl, having one to three substituents which are independently selected from the group consisting of hyrogen, halo, hydroxyl, nitro, trifluoromethyl, C1-C6 straight or branched alkyl or alkenyl, C1-C4 alkenyloxy, phenoxy, benzyloxy, and amino;
X is O, NH, NR1, S, CH, CR1, or C(R1)2;
Y is a direct bond, or a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C3-C8 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR2, S, SO, or SO2, where R2 is selected from the group consisting of hydrogen, (C1-C4)-straight or branched chain alkyl, (C3-C4)-straight or branched chain alkenyl or alkynyl, and (C1-C4) bridging alkyl wherein a bridge is formed between the nitrogen and a carbon atom of said alkyl or alkenyl chain containing said heteroatom to form a ring, wherein said ring is optionally fused to an Ar group; and
Z is an aromatic or tertiary alkyl amine oxidized to a corresponding N-oxide, wherein the aromatic amine is Ar oxidized to a corresponding N-oxide where Ar is a mono-, bi- or tricyclic, carbo- or heterocyclic ring, wherein the ring is either unsubstituted or substituted in none to three position(s) with halo, hydroxyl, nitro, trifluoromethyl, C1C6 straight or branched chain alkyl or alkenyl, C1-C4 alkoxy, C1-C4 alkenyloxy, phenoxy, benzyloxy, amino, or a combination thereof; wherein the individual ring sizes are 5-6 members; wherein the heterocyclic ring contains 1-6 heteroatom(s) selected from the group consisting of O, N, S, and a combination thereof wherein at least one of the heteroatoms is N, and wherein the alkyl amine is oxidized to a corresponding N-oxide where alkyl is a C1-C6 straight or branched chain alkyl or alkenyl which is optionally substituted in one or more positions with C1-C6 straight or branched chain alkyl or alkenyl, or C1-C9 cycloalkyl, or C5-C7 cycloalkenyl, or hydroxyl, or carbonyl oxygen, or with Ar, where said alkyl, alkenyl, cycloalkyl, cycloalkyl, or Ar group is optionally substituted with C1-C4 alkyl, C1-C4 alkenyl, or hydroxy, or carbonyl oxygen, or wherein any of the carbon atoms of said alkyl, alkenyl, cycloalkyl, cycloalkenyl, or Ar group is optionally replaced with O, NH, NR1, S, SO, or SO2; and,
R1 is hydrogen, (C1-C4)-straight or branched chain alkyl, (C3-C4)-straight or branched chain alkenyl or alkynyl, or R1 is Y-Z, as defined above.
In preferred embodiments, Ar is selected from the group consisting of pyrrolidinyl, pyridyl, pyrimidyl, pyrazyl, pyridazyl, quinolinyl, and isoquinolinyl.
Particularly preferred compounds of the present invention include:
3-(2-3Pyridyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-oxide;
3-(3-Pyridyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-oxide;
3-(4-Pyridyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-oxide;
3-(2-Quinolyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-Oxide;
3-(3-Quinolyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-oxide; and
3-(4-Quinolyl)-1-propyl(2S)-1-(3,3-Dimethyl-1,2-dioxo-pentyl)-2-pyrrolidinecarboxylate, N-oxide.
The present invention also relates to a pharmaceutical composition comprising a neurotrophically effective amount of the compound of formula I, II, III, or IV, and a pharmaceutically acceptable carrier.
The present invention further includes methods of using the compounds of the present invention. One preferred embodiment includes a method of stimulating damaged neurons in an animal, comprising:
administering to the animal neurotrophically effective amount of a compound of the present invention.
Another preferred embodiment of the present invention includes a method of promoting neuronal regeneration in an animal, comprising:
administering to the animal a neurotrophically effective amount of a compound of the present invention.
Yet another embodiment of the present invention includes a method of preventing neurodegeneration in an animal, comprising:
administering to the animal a neurotrophically effective amount or a compound of the present invention.
Another embodiment includes a method of treating neurological disorders in an animal, comprising:
administering to the animal a neurotrophically effective amount of a compound of the present invention.
The neurological disorders for which the compounds of the present invention are particularly useful are selected from the group consisting of: peripheral neuropathy caused by physical injury or disease state, physical damage to the brain, physical damage to the spinal cord, stroke associated with brain damage, and neurological disorder relating to neurodegeneration. Examples of neurological disorders relating to neurodegeneration are Alzheimer""s Disease, Parkinson""s Disease, and amyotrophic lateral sclerosis.